266 CONSIDERATION OF CARBON COMPOUNDS. 



lent solvent for many organic substances, as fats, resins, gutta- 

 percha, etc., and also for iodine, sulphur, phosphorus, etc. 



Volatile or essential oils. The term essential oil is more a 

 pharmaceutical than chemical term, and is used for a large 

 number of liquids obtained from plants, and having in common 

 the properties of being volatile, soluble in ether and alcohol, 

 almost insoluble in water, and having a distinct and in most cases 

 even highly characteristic odor. They stain paper in a similar 

 manner as fats or fat oils, from which they differ, however, 

 by the disappearance of the produced stain after some time, 

 whilst fats leave a permanent stain. 



In their chemical composition essential oils differ widely; 

 some are compound ethers, others aldehydes, but most of them 

 are hydrocarbons or oxidized hydrocarbons. 



Many essential oils have the composition C 10 H 16 , or the poly- 

 meric composition C 20 H 32 . Of essential oils having the com- 

 position C 10 H 16 , may be mentioned the oils of turpentine, juniper, 

 lemon, rosemary, bergamot, lavender, etc. The products of oxida- 

 tion (either found in the plant itself or formed by the subsequent 

 action of the oxygen upon the oils) have often the composition 

 C 10 H 16 O or C 10 H 14 0, but compounds of the composition C 10 H 16 H 2 O 

 or C 10 H 18 and C 10 H 18 H 2 are also found ; the two latter sub- 

 stances, for instance, in the oil of peppermint. 



Camphors are substances closely related to the volatile oils, 

 both in chemical and physical properties. Borneo-camphor has 

 the composition C 10 H 18 0, whilst the camphor found in the cam- 

 phor-trees of China and Japan has the composition C 10 H 16 0. 



Resins are obtained, together with the essential oils, from 

 plants. Mixtures of a resin and a volatile oil are known as 

 oleo-resins, while mixtures of a resin or oleo-resins and gum are 

 known as gum-resins. The name balsam is also used for a certain 

 group of oleo-resins. 



The resins are mostly amorphous, brittle bodies, insoluble in 

 water, but soluble in alcohol, ether, fatty and essential oils ; they 

 are fusible, but decompose before being volatilized; they all 

 contain oxygen and exhibit somewhat acid properties. 



Turpentine, the oleo-resin of the conifers, contains besides the 



